How well does mammography work in women with dense breasts?

Dr. Deanna J. Attai, MD

Screening mammography is one-size-fits-­all, but breast cancer risk is not. Breasts are made of fat and glandular tissue. The more glandular tissue you have, the denser your breasts. Studies show that women with dense breast tissue have a higher risk of developing breast cancer.

It is more difficult for a radiologist to spot a potential tumor in dense breast tissue than less dense tissue, which means cancer may be missed during mammography. Some state laws require that women be informed if a mammography shows they have dense breast tissue. This legislation is intended to encourage women with dense breast tissue to discuss breast cancer risk and screening with their doctors. Such information is part of a growing trend aimed at individualizing breast cancer screenings.

This content originally appeared online at UCLA Health.

In women with very dense breast tissues, reading a mammogram is like looking through a snow storm. It’s just a white blanked out tissue, so it’s very, very difficult to read a mammogram through very dense breast tissue. In those women, it's recommended that they get a follow-up ultrasound or tomosynthesis as a second way for the doctor to look at the breast tissue.

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Breast density is something that should be taken into consideration when planning mammography screening. The density of a woman's breast is dependent on multiple factors, the greatest being age, as younger women tend to have a higher level of density. This is important to understand as increased density in a person's breast will decrease the sensitivity of mammography. Along with this, women with increased breast density also have a greater incidence of breast cancer. Studies have shown a significant improvement in breast cancer identification in patients with less dense breasts. In some scenarios it may be beneficial to use different methods, such as ultrasound, or a combination of methods, if the woman's breast tissue is dense. 

In light of the availability of other imaging tools, it is important to consider how sensitive mammography is, and to understand its benefits and limitations. The sensitivity of mammography decreases as the density of the breast increases. As women age, their breasts become less dense and more fatty, which is why a mammogram is recommended for women ages 40 and up. Mammograms reveal the density of breast tissue, which is graded on a four-stage scale. 

Category 1 tissue consists of mostly fat, while category 4 tissue contains little fatty tissue, and almost all fibroglandular tissue. Mammography is 98% sensitive in women with fatty breasts, and 84% sensitive in women with dense breasts. In women under age 50 with a family history of breast cancer, studies have shown that the sensitivity of mammography can be as low as 70%.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.